A planer flattens the top surface of a board fedd through the machine. Along with a jointer, the planer is used for milling boards.
Spiral Cutter Head
Traditional planers use a small number of knives the run the entire width of the cutter head to make the cut. Sprial cutter heads use a large number of small cutters arranged in a spiral fashion on the cutter head.
A spiral cutterhead cuts cleaner than a traditional cutterhead, last longer, and is easier to set up. Unfortunately it is also much more expensive. A spiral cutterhead is a good option for a heavily used planer.
1) Choose a maximum stock width
The width of the machine limits the maximum width of boards that can be fed through this machine. No single size fits everyone, because planers go up in price as planing width increases.
2) Choose a power level
Planers take large, aggressive bits out of the workpiece. They require large, powerful motors to do their work. If you plan on planing wide boards on a regular basis, you should look for a more powerful planer.
3) Choose your cutter head
A spiral cutterhead produces a better cut than a traditional cutterhead, but cost significantly more. Some machine can be retrofit with a spiral cutterhead after the fact. If you plan on milling a lot of boards with your planer, investing into a spiral cutterhead is a good choice.